1. Field of the Invention
The present invention relates to an LED (Light Emitting Diode) light converting resin composition, and an LED member using the same. More particularly, the present invention relates to a LED light converting resin composition obtained by mixing a heat-resistant transparent matrix resin with a color converting fluorescent substance, and a light diffusing bead, optionally together with a pigment, and an LED member using the same, such as an LED lens or a light guide plate.
2. Description of the Prior Art
An LED is a kind of semiconductor device which converts electrical energy to light energy by using a characteristic of a semiconductor including a specific compound. The LED is advantageous in that its power consumption is very small due to high photoconversion efficiency, it is appropriate for miniaturization, slimming, and light-weighting, due to its small size light source and at the same time can be unlimitedly extensibly provided, it has a semi-permanent and long life (a blue, violet, or UV LED has a life of about 100,000 hours, and a white LED has a life of about 30,000 hours), it has a very high response speed due to no need for pre-heating because it does not use thermoluminescence or electroluminescence, it has a very simple lighting circuit, it has high impact resistance, safety, and few environmental polluting factors because it does not use discharge gas and a filament, it can perform pulsed-operation with a high repetition rate, it reduces fatigue on an optic nerve, and it can realize full color. Accordingly, the LED is widely used for a light source for a liquid crystal display (LCD) back light of a cellular phone, a camcorder, a digital camera, a personal digital assistant terminal (PDA), etc., a traffic light, an electronic display board, a car headlight/taillight, a display lighting lamp of various kinds of electronic devices, office machines, a Fax, etc., a night lighting of a remote control or a surveillance camera, infrared communication, an information display of an outdoor advertising board using various combinations of RGB pixels, an ultra-precision display of an electronic display board, and high-class indoor/outdoor lighting. Especially, a high-brightness LED in which a general problem found in a conventional LED, such as a low brightness, has been improved, has been commercially available, and its purposes and applicable devices have been rapidly expanded.
Especially, since a white LED is very useful as a light source for an LCD back light, and an indoor/outdoor lighting, its usage frequency has been rapidly increased. Also, in like manner as an incandescent lamp shows a tendency to be driven out from a market by a fluorescent lamp, it is expected that the LED will sweep over a lighting market within a short period of time.
A method for obtaining a white light by an LED is described below.
First, there is a classical method for obtaining a white light by combining three LEDs of red, green, and blue. The method has a problem in that it requires a relatively high manufacturing cost, increases the size of a product due to a complicated operating circuit, and degrades an optical characteristic and reliability of the product due to a difference in the temperature characteristics of three LEDs, and thus is hardly used at present.
There has recently been another method for obtaining a white light, in which a white LED is selected as a single LED for generating a white light, the surface of the white LED is coated with a fluorescent substance or the white LED's peripheral or lens is molded by being mixed with a fluorescent substance, a light generated by the single LED with a specific wavelength excites the fluorescent substance to generate a light with another wavelength, and the generated light is mixed with the light generated by the single LED chip.
However, in such a conventional method, the surface of a blue, violet, or UV LED is directly coated with a fluorescent substance or the LED's peripheral or lens is molded by being mixed with a fluorescent substance. Thus, the method has a problem in that the life of the LED is significantly reduced to one third or less due to LED degradation caused by a reduction in heat dissipation. Especially, if the fluorescent substance is not very homogeneously coated or dispersed/distributed, the luminescent color becomes inhomogeneous. However, it is very difficult to achieve homogeneous coating or dispersion/distribution of the fluorescent substance.
U.S. Pat. No. 5,998,925 (Nichia Corp.) discloses a widely practically used and oldest-type white LED, in which an InGaN-based blue LED with a wavelength of 450 nm is coated or molded with a yellow fluorescent substance (in general, yttrium-aluminum-garnet:Y3Al5O12:Ce, YAG-based compound), and a blue light of the blue LED excites the YAG yellow fluorescent substance. This allows the two wavelengths including the narrow-peak blue light of the blue LED, and the wide-peak yellow light of the YAG-based yellow fluorescent substance, to be recognized as a white light by human's eyes through complementary interference.
However, the white light includes mixed-lights having two wavelengths with incomplete complementarity, and thus has only a part of a visible region spectrum. For this reason, the white light has a color rendering index (CRI) of about 60˜75, and is generally not recognized as a near-natural white light. Thus, it does not satisfy a general indoor lighting. Also, there is a problem in that the luminance is low because the blue LED shows the highest efficiency at an excitation light source of about 405 nm while the YAG-based fluorescent substance is excited by a blue light of 450˜460 nm. Especially, in coating or molding of the YAG-based fluorescent substance, it is difficult to guarantee a homogeneous and uniform dispersibility. This reduces the uniformity and reproducibility of a product, and significantly reduces the life of an LED, in the luminance and spectral distribution of a white light.
In order to overcome the problems of the white LED including the blue LED and the YAG-based fluorescent substance, there has been suggested another-type of white LED. U.S. Pat. No. 5,952,681 (Solidlite Corp.) discloses a technology of obtaining a three-wavelength high-CRI near-natural white light by using a high-luminance UV LED with a wavelength of 250 nm˜390 nm as an excitation light source, and combining red, green, and blue fluorescent substances. However, the utilization of the white LED has a problem in that the blue and green fluorescent substances show a satisfactory light-emitting efficiency while the red fluorescent substance shows a low light-emitting efficiency. Especially, in a case of the UV LED, an organic resin is deteriorated by UV with a strong energy, thereby significantly reducing the life of the LED.
There is another type of white LED (Solidlite), which uses a violet LED with a wavelength of 390 nm˜410 nm, and obtains a white light by combining red, blue, and green fluorescent substances. The high-luminance violet LED is commercially available from Cree Corporation (U.S.), and is known to emit a relatively natural three-wavelength white light through uniform light-emission of red, blue, and green fluorescent substances by the violet light with 390˜410 nm.
Factors having an influence on the characteristics of a white light emitted from a white LED element may include the intensity of the LED-emitted light, combination applicability of the light emitted from the LED and the light fluorescent-converted by a fluorescent substance, and the component, the content, and the dispersed state of the fluorescent substance. These factors have a significant influence on an emitted light. Especially, a white light emitted by the blue LED and the YAG-based fluorescent substance may have a problem in that the emitted color is generally inclined to blue or yellow due to the difficulty in the additive amount adjustment and the homogeneous dispersion of a yellow fluorescent substance.
In order to obtain a white LED having a high light-emitting characteristic, a fluorescent substance has to be homogeneously dispersed in a light-transmissive matrix resin. However, in a fabrication process, before the matrix resin is completely hardened, a fluorescent substance with a much higher specific gravity (specific gravity of about 3.8˜6.0, but dependent on the kind of the fluorescent substance) is precipitated in the lower portion of light-transmissive matrix resin with a low specific gravity (e.g., an epoxy resin has a specific gravity of about 1.1˜1.5). Thus, it is difficult to obtain a white light having a high light characteristic. Furthermore, it is not easy to precisely control a degree of dispersion of a fluorescent substance. Accordingly, there is a problem in that it is not easy to fabricate a high-quality white LED device, and the fabrication reproducibility is not good.
Meanwhile, an LED lighting device employs an LED lens so that the light diffused and emitted from the LED through voltage application can be a parallel beam, and the intensity of the radiation can be increased within a view angle. Also, the view angle is adjusted by controlling curvatures of a light-incidence lower surface of the lens, and a light-emission upper surface of the lens. Also, it may be appropriately selected and used from various shapes, and sizes of lenses according to various parameters, such as the kind and power of a used LED, the use purpose, the preference of an end user, and the required intensity of the lighting.
FIG. 8 shows a sectional view of a conventional LED lens and FIGS. 9a to 9c show photographs of conventional various types of LED lenses 10′, 10a′, 10b′, and 10c′, respectively. The conventional LED lenses 10a′, 10b′, and 10c′ are generally hemisphere-shaped with a wide upper part and a narrow lower part, but are not limited thereto. They may take very various shapes. The lenses have upper surfaces 11a, 11b, and 11c formed with an annular lateral portion 11 and a flange 14, and a cylindrical LED mounting portion 13 formed at the bottom thereof. The upper portion of the LED mounting portion 13 may be formed into a flat shape, but is generally formed with an internal convex portion 12 for condensing.
The LED lenses 10′, 10a′, 10b′, and 10c′ may have a pectination upper surface 11a for making an emitted light to be mild, a multiple-dot type upper surface 11b, or a slippery smooth upper surface 11c. Also, the upper surface may have an opening at the center thereof, and the lateral portion 11 may have various angle-gradients and lengths for adjustment of an irradiation angle. Also, the upper surfaces 11a, 11b, and 11c may be formed into a forward-projecting convex shape, a flat shape, a concave shape, or another specific shape.
The reference numeral 30 denotes a substrate and the reference numeral 40 denotes a light diffusing lens for LED element molding.
FIG. 10 shows a photograph of an example of a conventional LED lighting device 60 employing a plurality of conventional LED lenses 4c. In the shown example, in a socket 50, the LED lighting device 60 is mounted. The plurality of LED lenses 4c, although not shown, are placed on a plurality of LED chips mounted on a substrate within the LED lighting device 60, respectively, and then are simply held and fixed by a front-side fixing plate without an additional adhesive.
FIG. 11 is an exploded sectional view showing a schematic structure of a conventional edge type back light unit.
As shown in FIG. 11, the conventional edge type back light unit 100′ includes a light source 115; a light guide plate 110′ having an one end portion opposed to the light source 115a, a reflection sheet located at a lower surface of the light guide plate 110′, a prismatic sheet 130 located at an upper surface of the light guide plate 110′, a light diffusing sheet 140 located at an upper surface of the prismatic sheet 130, and a protective sheet 150 located at an upper surface of the light diffusing sheet 140.
More concretely, the light source 115 consists a linear light source 115a or a white LED (not shown). Also, the light source 115 having a reflection plate 115b is opposed to a thick side surface of the light guide plate 110′ of a taper-shape. The reflection sheet 120 is located at the lower surface of the light guide plate 110′ and the light diffusing sheet 140 and the protective sheet 150 are laminated the upper surface of the light guide plate 110′ in order. The prismatic sheet 130 has a plurality of prismatic patterns (not shown) parallel to each other.
Also, a light emitting surface 111 is formed on the upper surface of the light guide plate 110′ and the reflection sheet 112 is bounded on the lower surface of the light guide plate 110′. Furthermore, a flat incident surface 112 is formed on one side surface adjacent to the light source 115. Also, a plurality of prismatic patterns 114 having prismatic slopes 114a and 114b are formed on the lower surface of the light guide plate 110′.
Here, the light irradiated by the light source 115 is accepted into the flat incident surface 112 and then, is scattered by the prismatic slopes 114a and 114b of the prismatic patterns 114 located on the lower surface 113 of the light guide plate 110′. Thereafter, it is emitted toward the prismatic sheet 130 through the light emitting surface 111 of the light guide plate 110′ and then, is again scattered by the prismatic sheet 130 having the plurality of parallel prismatic patterns (not shown) perpendicular to the prismatic patterns, which is located on the lower surface 113 of the light guide plate 110′. Finally, the light is converted into a homogenized light through the light diffusing sheet 140 to be outputted.
However, since the light diffusing sheet 140 serves to convert the incident light into the homogenized light over the entire area of the display panel through the diffusion and scattering thereof, in the conventional back light unit, there are problems in that the thickness thereof is increased and durability and economic feasibility thereof is deteriorated owing to increase of man-hour and number of parts.